1. Field of the Invention
This invention relates to an installation for replacing live rolls in a mill stand and, in particular, in a skin-pass stand.
2. Background of the Invention
As is known, a rolling mill generally comprises at least two superposed rolls inside a fixed stand, the axes of the rolls being parallel and located in a substantially vertical plane. "Two-high" stands, for example, comprise only two rolls, with the product to be rolled passing between them. In "Four-high" stands, the product to be rolled passes between two live rolls of relatively small diameter which bear directly on two pressure rolls. In "Six high" stands, the corresponding pressure roll. Other types of rolling mil comprising a greater number of rolls are also known
The main purpose off "skin-pass" rolling mills is not to reduce the thickness of the product, but only to modify the surface state or metallurgical properties of an already rolled strip. A skin-pass stand is generally made up in the same way as a four-high stand, with two live rolls surrounded by two pressure rolls.
The live rolls, which are in contact with the product, wear relatively quickly.. It must also be possible to adapt the diameter of these live rolls to the nature and thickness of the product to be rolled and, in certain cases, to the surface state required. The rolls must therefore be periodically replaced.
It is also known that the mill rolls must be driven in rotation and that the driving torque may be applied either directly on to a live roll or on to one of the pressure rolls which then drives the corresponding live roll in rotation by friction. Each mill stand is therefore associated with drive means connected to the driven roll by a spindle having universal joints at its ends. This is why the roll replacement device is generally placed on the operator side, i.e., on the side opposite the drive means.
Various arrangements have been used up until now to replace live rolls.
Generally, each end off each roll turns in a chock which forms a centering fork for the roll, and on which forces can be applied to tighten or strain the roll. To be able to remove and introduce the rolls together with their chocks, the chocks often are provided with rollers that roll on rails provided on the fixed uprights of the sand and parallel to the axes of the rolls.
To withdraw a roll of to place it back in position, a balanced "C-shaped" hanging device can be used, for example, carried by a traveling crane, and which comprises a part that penetrates into the axis of the roll in order to lock onto it.
In another arrangement, described in document JP-A-61.286.008, use is made of a magazine arranged next to the stand, mounted so as to rotate about an axis parallel to the axes of the rolls and comprises a number of compartments in which replacement rolls are stored, one of these compartments being empty.
The magazine is first of all rotated about its axis until the empty compartment is aligned with the roll to be replaced in its working position in the stand. A transfer means associated with the magazine then locks onto one end of the roll to be replaced, withdraws it from the stand and places it in the empty compartment.
The magazine is then rotated about its axis until a replacement roll stored in another compartment is aligned with the working position. The transfer means then pushes the replacement roll into its working position on the stand.
In the case of a skin-pass stand, such roll changes are called for relatively frequently, so that rolls can be taken to the workshop for reconditioning or placed in store temporarily and replaced by other rolls according to program changes, for example in order to obtain another state of roughness on the strip or change the diameter of the rolls.
In addition, the current practice is to make metal strip processing lines operate continuously, consisting in particular of one or more skin-pass stands using strip accumulators which make it possible to intervene on one part of the installation for the purposes of a repair or a replacement without stopping the feeding of the strip through the other parts.
However, these accumulators have only a limited capacity, which means that it is important to keep the intervention time as short as possible.
In a rolling mill installation comprising several stands placed sequentially in the product feed direction, it would be attractive to use a mobile roll replacement device comprising a roll support platform, placed at the desired height, and capable of moving on rails parallel to the feed direction along one side of the stands so as to take up position in front of one of these stands.
In an arrangement of this type described, for example, in GB-A-2.226.265, the two live rolls placed inside the stand form a superposed assembly which, through roll lets provided on the chocks of the lower roll, rolls on two rails fixed to the stand and parallel to the axes of the rolls. This stand is also associated with an auxiliary bench placed on the other side of the rolling track of the roll replacement device. This auxiliary bench carries two rails on which a pair of superposed reserve rolls are mounted in the manner described above.
The roll replacement device comprises a platform which turns about a vertical axis, and on which two pairs of parallel rails are provided, arranged symmetrically on each side of the axis. In the replacement position, these rails are aligned, respectively, with the fixed rails of the stand and the fixed rails of the bench, the latter being longitudinally offset with respect to the stand.
Two transfer means, rolling in opposite directions, respectively, on the two pairs of rails of the rotary platform, make it possible to bring the rolls to be replaced which are withdrawn from the stand and the replacement rolls which are withdrawn from the auxiliary bench, onto the rotary platform at the same time. A 180.degree. rotation of the platform makes it possible to reverse the arrangement and, by moving transfer means in the opposite direction, to introduce the replacement rolls into the stand and move the worn rolls previously withdrawn from the stand onto the bench.
Although rolls can be rapidly replaced using such an arrangement, the pair of replacement rolls has to be selected in advance and placed on each stand's auxiliary bench. The assembly is therefore very bulky and makes the mill stands difficult to access, the device being placed, as customary, on the operator side.
Moreover, several roll handling operations are involved, with each pair of used rolls having to be transported to a maintenance and storage zone and then replaced by new rolls.
Even if such a device is used, the worn rolls have to be picked up again and deposited in a maintenance and storage zone from where new rolls are taken and [)laced on the auxiliary bench.
These handling operations are time consuming and expose the rolls to risks of accidental damage as they are moved.
Skin-pass rolling mills, where live rolls have to be changed relatively often in line with manufacturing programs, require many such handling operations.
The invention offers a solution to all these drawbacks I 0 thanks to a new mill roll replacement installation designed to reduce the number of handling operations, and as a result reduces the risk of rolls becoming damaged, and which also gives a wider choice of replacement rolls.
In addition, the invention makes it possible to replace rolls in a very short space of time and without stopping the feeding of the rolled strip.